Conventionally, an internal combustion engine has a supercharging device such as a turbocharger for supercharging intake air, which is drawn into a cylinder of the engine using a turbocharger, to increase output power of the engine or to reduce fuel cost. Here, the turbocharger has a turbine, which is rotated utilizing exhaust energy of the engine, thereby operating a compressor arranged coaxially with the turbine, so that the turbocharger supercharges the intake air. In this turbocharger, increase in supercharging pressure in a low rotation range of the engine may be insufficient, consequently, the actual supercharging pressure may decrease. As a result, charging efficiency may decrease, and enhancement in the engine output may become insufficient.
According to JP-A-1-117932 and JP-B2-P3092206, an electric motor is mounted to a shaft for connecting the turbine and the compressor, so that the insufficient amount of the actual supercharging pressure is supercharge-assisted by the electric motor in the low speed rotation range of the engine. An electrically operated generator is used as the electric motor. The actual supercharging pressure can be increased in a high speed rotation range of the engine, even when no supercharging assist is performed. Hence, regenerative electric power can be also generated in the electrically operated generator by rotating the electrically operated generator via the turbine and the shaft utilizing the exhaust energy of the engine.
However, in the above engine control system with the above supercharging device, the electric power regeneration using the electrically operated generator is performed in only the high speed rotation range of the engine. However, for example, high speed range may not be used in normal running in a high speed diesel engine for a passenger car. Therefore, in this method, it almost has no benefit of the electric power regeneration using the electrically operated generator. Namely, it almost has no benefit for enhancing fuel efficiency by improving efficiency, in comparison with the electric power generation of an alternator that serves as an engine auxiliary device rotated and operated by the engine.
Therefore, for example, it is conceived that the effect of the improvement in fuel efficiency can be also obtained by performing the electric power regeneration using the electrically operated generator in the low speed rotation range or a light load range. These low speed rotation range and light load range are in a normal range of the diesel engine for a passenger car. However, when the electric power regeneration is performed by rotating the electrically operated generator utilizing the exhaust energy in either the low speed rotation range or the light load range, a part of the exhaust energy is consumed in the electric power regeneration. Therefore, the supercharging effect may be correspondingly decreased, and the output shaft torque of the engine (engine torque) may be decreased.
Here, an exhaust gas recirculating device (EGR device) may be mounted for reducing highest combustion temperature by mixing a part of the exhaust gas of the engine into the intake air, thereby reducing a harmful substance (e.g., NOx) included in the exhaust gas, and improving an exhaust gas purifying performance. The EGR device has an exhaust gas return flow pipe (EGR pipe) for returning a part of the exhaust gas of the engine from an engine exhaust pipe into an engine intake pipe. The EGR device also has an exhaust gas return flow rate control valve (EGR control valve) for controlling an exhaust gas return flow rate (EGR rate), which represents a rate of exhaust gas flowing into this EGR pipe.
In recent years, a performance for treating exhaust gas needs to be further improved by flowing a large amount of exhaust gas recirculating gas (EGR gas), in the diesel engine. This EGR gas returns to the engine intake pipe through the EGR pipe. Therefore, an intake shutter becomes practically used for throttling an intake passage on the upstream side of a joining portion, in which the new intake air merges with the EGR gas, with respect to an airflow direction. That is, intake shutter is arranged on the side of the turbine of the turbocharger with respect to the joining portion in the intake passage. Thus, the flow rate (new intake air amount) of the intake air supercharged by the turbocharger, when the EGR control valve opens, can be reduced.
It is conceivable to combine the above EGR device and the intake shutter with the above engine control system having the supercharging device to construct a diesel engine control system having a turbocharger. When the opening degree of the EGR control valve is constant in the EGR device, it is generally known that as negative pressure in the intake pipe on the downstream side of the intake shutter with respect to the airflow direction decreases, the EGR flow rate increases and a performance for purifying the exhaust gas can be enhanced. Thus, the reducing effect of the harmful substance can be improved.
In this diesel engine control system having the turbocharger, when the electric power regeneration is performed by rotating the electrically operated generator utilizing the exhaust energy while the EGR control valve opens, the amount of electric power generated using the electrically operated generator increases as the rotation speed of the electrically operated generator or the turbocharger increases. Further, as the amount of electric power generated using the electrically operated generator increases, resistance arises in rotation of the turbine and the compressor of the turbocharger. This resistance becomes the resistance (load) of the intake air drawn from the compressor of the turbocharger into the cylinder of the engine, consequently, the amount of intake throttling increases and the intake pressure decreases. Thus, since the intake pipe pressure decreases, the exhaust gas of the engine easily returns to the engine intake pipe, even when the opening degree of the intake shutter is not corrected to the closing side. Therefore, the engine torque may decrease for an amount of this exhaust gas returning to the engine intake pipe.